In mid-March 1982 we had 3 rambutan trees beginning to mature fruit at Kamerunga Horticultural Research Station. One tree had fruit ripening slightly ahead of the others. Quite a number of fruit on this tree were being eaten by flying foxes, so we decided to try carbide as a deterrent. We had heard that carbide, when hung in a tree, prevented fruit damage, but I had thought it was most likely an old wives tale - or only partly effective.
We placed a piece of rock carbide (approx. 60g) in a perspex container (which was relatively waterproof but had vents to allow acetylene gas to disperse) and hung in the centre of the tree.
Incidence of flying fox damage stopped over-night and this must be regarded as fairly substantive evidence of carbide effectiveness, since usually damage to fruit increases after initial flying fox invasion.
We provided carbide containers for the other two adjacent trees and the overall result was less than 3% damage to the total crop. However, an additional tree (without carbide) some 50 metres away, has had every maturing fruit taken by flying foxes. In fact, they have taken quite immature fruit.
It will be interesting to look at the effect of carbide on damage to litchis, next season. If the treatment works then undoubtedly it will be a very economic control, even if every tree has to be provided with a carbide container.
The container must be one which will prevent rain reaching the carbide and dissipating it too quickly, yet having ventilation. A 60g piece of rock carbide appears to last 6 to 10 days - varying according to humidity.
The other story concerns strobe lights. In 1981 a New South Wales company started to market the lights, which had reputedly performed very well in deterring attacks on fruit in trials conducted in the Sydney area.
A few of the lights were purchased by North Queensland litchi growers, but most were installed in orchards after fruit had reached the green-mature size. Results were not encouraging, and in some situations, completely ineffective. However, one Cairns grower observed a lessening in damage toward the end of his crop. It may well be that the lights have to be operated well in advance of fruit maturity.
In any event use of carbide and strobe lights will appeal to all nature lovers, and we in the D.P.I. would be pleased to hear reports of results of their use.
DATE: May 1982
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